Celestron EdgeHD8, 0.7 focal reducer, OAG owners

[ncwolfie]

I'm in desperate need of advice here. Have read all the threads about the 105mm back focus when using a the Celestron edgehd8, celestron 0.7 focal reducer. Of course these two in combination yield the perfect 105mm back focus when using a DSLR. As most of you know, the problem arises when using an OAG. Basically it won't work. I was under the impression that this would work with a Thin OAG, so I purchased the orion thin OAG.

I will be using a ASI 120MM-s as an autoguider.  But before I can determine the spacers I will need there, how is it possible to insert a thin OAG between the celestron T adapter and the camera without exceeding the 105mm backfocus.

It appears that if there was a way to reduce the T adapters length, then I could determine spacers to do the rest.

(See the Celestron focal reducer diagram below)

 

I'm in a pickle here and really need to know how others have overcome this, what you used or if it is even possible?

I'm to the point I either have to get a solution or try and sell the Thin OAG and go the guidescope route, something I did not want to do.

I currently have 56.5mm from the OAG prism to the ASI camera chip. That is a minimum distance and cannot be changed, so it would seem to me that I would need to reduce the length near the T adapter to rein in the guide came distance

to come close to 105mm. But when doing that what I loose in distance at the t adpter, I may need to add a spacer or not on the other side of the Thin OAG before the DSLR to maintain 105mm.

So unless I am seeing this wrong, the culprit is the T adapters length?

Any advice would be greatly appreciated.

[alexjj67]

I have just had the same problem you have. I have a camera with a back focus of 17mm, OAG of 24mm and Filter wheel of 22mm. Adding up to 63mm. With only 55mm to play with as the t-adapter is 50mm long.

I was more worried about my imaging camera than the guide camera. I am using an atik OAG and that had a fair bit of play

I am fortunate to have a friend who has his own engineering company and he made me a 42mm extension piece out of aluminium with the correct size threads on either end.  That replaced the t-adapter.

If you don't know anyone who could make it the link below will get it done but they aren't cheep. 

http://www.preciseparts.com/ppmain/index.html

Alex

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[ncwolfie]

Bookmarked this site for future reference in case do end up needing it. Thats' a great find Alex.

[rockyraccoon]

Custom T2 extensions can be found easily and cheaply on most astronomy gear websites (optcorp, agena, etc)

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